    // --------------------------------------
    // i2c_scanner
    //
    // Version 1
    //    This program (or code that looks like it)
    //    can be found in many places.
    //    For example on the Arduino.cc forum.
    //    The original author is not know.
    // Version 2, Juni 2012, Using Arduino 1.0.1
    //     Adapted to be as simple as possible by Arduino.cc user Krodal
    // Version 3, Feb 26  2013
    //    V3 by louarnold
    // Version 4, March 3, 2013, Using Arduino 1.0.3
    //    by Arduino.cc user Krodal.
    //    Changes by louarnold removed.
    //    Scanning addresses changed from 0...127 to 1...119,
    //    according to the i2c scanner by Nick Gammon
    //    http://www.gammon.com.au/forum/?id=10896
    // Version 5, March 28, 2013
    //    As version 4, but address scans now to 127.
    //    A sensor seems to use address 120.
    // Version 6, November 27, 2015.
    //    Added waiting for the Leonardo serial communication.
    //
    //
    // This sketch tests the standard 7-bit addresses
    // Devices with higher bit address might not be seen properly.
    //
     
    #include <Wire.h>
     
     
    void setup()
    {
      Wire.begin();
     
      Serial.begin(9600);
      while (!Serial);             // Leonardo: wait for serial monitor
      Serial.println("\nI2C Scanner");
    }
     
     
    void loop()
    {
      byte error, address;
      int nDevices;
     
      Serial.println("Scanning...");
     
      nDevices = 0;
      for(address = 1; address < 127; address++ )
      {
        // The i2c_scanner uses the return value of
        // the Write.endTransmisstion to see if
        // a device did acknowledge to the address.
        Wire.beginTransmission(address);
        error = Wire.endTransmission();
     
        if (error == 0)
        {
          Serial.print("I2C device found at address 0x");
          if (address<16)
            Serial.print("0");
          Serial.print(address,HEX);
          Serial.println("  !");
     
          nDevices++;
        }
        else if (error==4)
        {
          Serial.print("Unknow error at address 0x");
          if (address<16)
            Serial.print("0");
          Serial.println(address,HEX);
        }    
      }
      if (nDevices == 0)
        Serial.println("No I2C devices found\n");
      else
        Serial.println("done\n");
     
      delay(5000);           // wait 5 seconds for next scan
    }
